In the sport of golf, one element of the game is to hit the ball as far as possible and as accurately as possible. Golf balls produced by different manufacturers or with varying history will respond in varying ways to being struck by the golf club; some will travel farther than others. A significant factor in determining how far a ball will travel after being struck is the COR of the golf ball. By selecting golf balls that have a higher COR, a golfer may have his ball travel farther, resulting in an advantage over his opponents. Alternatively, a golfer may select balls that have closely matched Coefficients of Restitution, such that his golf balls will travel in a more predictable trajectory.
The United States Golf Association (USGA) performs tests of Coefficient of Restitution on golf balls. The equipment consists of an impact device driven to a known velocity, which then strikes the golf ball. Velocity of the golf ball is measured and is interpreted for the Coefficient of Restitution of the golf ball.
The American Society for Testing and Materials (ASTM) has a method defined in its standard F1887, Standard Test Method for Measuring the Coefficient of Restitution (COR) of
Baseballs and Softballs. In the ASTM method, baseballs or softballs are propelled at a known velocity in a manner to strike a rigid plate. The rebound velocity is measured and is interpreted for COR of the baseball or softball. In the ASTM method, the apparatus propelling the baseball or softball requires the ball be launched with a speed accuracy of approximately 1%. Both the ASTM method and the USGA method require skilled operators and are impractical, cumbersome and excessively costly to be employed by the average sportsman or golfer.
Dr. Ian Plummer of the Oxford University croquet club has described a method used to measure the COR of croquet balls. The rebound height of the ball is measured and is interpereted for COR.
An Australian team of Richard Bowman, Peter Westgate and Elizabeth Maliwat, CSIRO Division of Building, Construction and Engineering, Highett, Victoria 3190, Australia describe a proposed procedure to test COR of ceramic tiles. The COR test apparatus consists of a ball-release apparatus, where an electromagnet releases a 19 mm diameter chrome steel ball that falls 1 meter onto the center of a horizontal test specimen that is clamped to a horizontal support base. A microphone and electronic timer computes the time interval between the first and second impacts of the dropped ball, to the nearest 0.001 second. According to their paper, the COR can be calculated from the relationship:COR=(1.226T^2)^0.5
U.S. Pat. No. 4,509,362 discloses a device in which COR is determined as a function of the height from which the ball is dropped to the rebound height. This method is not complex, but requires careful measurement by the observer, and is not easily and routinely done. In addition, it is prone to human error in observation of the rebound height.
U.S. Pat. No. 5,245,862 teaches a testing device in which the COR is determined by comparison of the bounce period of successive bounces of the ball.
These and other devices which have been proposed to test golf balls and the like are cumbersome and not suitable as compact, portable testing devices which can be easily carried and stored with other golf equipment and which can be used before and during play.